Found another website from Austria that uses Solar, Heat Pump, large uninsulated underground storage tank, which is allowed to freeze some (latent heat).
Nice simple design presented well.
Their house needs 18,000 KWH of heat (61.42 million btus) per year, about 1.3 x my house design.
http://punktwissen.at/pdf/punktwisse...System-LEO.pdf
and
https://elkement.wordpress.com/tag/heat-pump/
and
https://elkement.wordpress.com/2013/...umps-are-cool/
They also have a DHW tank with internal HX kept @ 50C (122F), which can be heated at a fairly high COP by Heat Pump, without fear of Legionella.
"Regarding the hydraulic design a question that comes up very often is about hot water heating:
You heat hot water indirectly by using a tank at 50°C? I don’t believe you that this is sufficient.
Believe me, it is. My very own very long and very hot showering – elementary showering as I call it – is a worst case test. The heat exchanger in this hygienic storage tank has an effective area of nearly 6m2 - that’s rather large, and this is crucial for a heat-pump-powered system.
The operating temperature of the heat pump should be kept as low as possible in order to obtain high coefficients of performance. Thus the temperature difference between tap water and heating water is rather low, and in order to compensate for that and still get reasonable heating powers the area of the heat exchanger should be big. The effective heating power of this heat exchanger is 12kW."